1. Field of the Invention
The invention relates to CRT display devices and in particular to means for reducing ambient light reflections from the CRT screens of such devices.
2. Description of Related Art
A common problem with CRT display devices, such as computer monitors and televisions, is disturbing reflections of ambient light from the luminescent screen of the CRT component utilized in each device. Such reflections reduce the contrast of the luminescent image produced by the CRT.
In order to attenuate these reflections, CRT faceplates are commonly made of tinted glass. Because the luminescent screen of a CRT is disposed on the inner surface of the faceplate, the reflected ambient light must pass through the thickness of the faceplate twice. The reflected ambient light is thus attenuated to a much greater extent than the light from the luminescent image produced on the screen, which passes through the faceplate only once.
Although this approach improves the visibility of the luminescent image, it has significant limitations. As the brightness of the ambient light radiation increases, so does that of its reflection. In order to maintain contrast, the brightness of the light from the luminescent image must be increased to predominate over the reflected light. In brightly lighted surroundings, the combined brightness levels of the luminescent image light and the reflected ambient light can be so high as to cause discomfort to the viewer.
Another limitation of the conventional tinted faceplate approach is the appearance it presents when the CRT is not in use. It is aesthetically desirable that the faceplate be dark when the CRT is off, but this cannot be achieved without tinting the faceplate to such a degree that it is virtually non-transmissive to ambient light reflected from the non-operating luminescent screen. Such a high degree of tinting is impractical, because it would severely attenuate the image from the operating luminescent screen when the CRT is on.